Composite wood products are generally formed from wood strands or the like bonded together by a suitable resin such as phenol formaldehyde (PF) or isocynate resins (MDI). The strands may be random or parallel oriented relative to one another and in some cases, the composite product is made from layers with different orientation or strands in adjacent layers.
These composite products find a variety of different usages, many of which are enhanced by providing the product with improved biodurability.
It has been shown in U.S. Pat. No. 4,879,083 issued Nov. 7, 1989 to Knudson et al. to apply anhydrous borax or zinc borate to the wood strand and bond the strands together into a composite product resistant to decay by insects and/or organisms using phenol formaldehyde as the binding agent. This teaching overcame a particular problem of the use of borax with phenol formaldehyde wherein the borax impeded the binding characteristics of the phenol formaldehyde.
It is also now known to add zinc borate to wood composites in conventional blending operations in processes using resins such as phenol formaldehyde as taught by Knudson et al. or other resins including isocynate resins for binding the strands for form the composite product resistant to biological degradation. Such addition of zinc borate in powdered form has been found to be difficult implement on a commercial scale as the powdered zinc borate and causes dusting and other problems regardless of the adhesive resin being used. For example, zinc borate sometimes absorbs liquid when MDI resin are used thereby reducing the internal bond of the product. Generally, the poor adhesion of the produced zinc borate causes waste and increase dust problem throughout the mill.